One type of prior art plumbing stop valve, which valve is in common use, has a metal valve stem in a metal valve body. The stem and body have large rectangular threads that matingly engage each other, and the stem has a seal at one end. The stem is rotated several turns to move to either the open or the closed position. A serious disadvantage of this type of stop valve is that after long periods of disuse, corrosive or mineral buildup on the threads causes the valve stem to freeze and thus renders the valve inoperable.
Efforts to develop a stop valve that does not freeze up are exemplified by U.S. Pat. Nos. 4,078,764 and 4,609,177. The stop valves disclosed in these two patents utilize rubber sealing member which closes the outlet opening by completely covering the opening. When the valve is in the closed position, water pressure forces the sealing member to bulge into the outlet opening causing difficulty in turning the stem from the closed position. In addition, the intersection between the outlet opening and the cavity containing the sealing member is a sharp edge which abrades the sealing members.
The bulging problem is eliminated by another type of prior art stop valve that utilizes a plastic valve body and a plastic stem. The plastic stem has an O-ring that can be made to surround the outlet opening to thus seal the outlet opening off from the inlet opening. The stem is rotated a fraction of a turn to move the O-ring to either the open or the closed position. Even with a plastic valve body, the O-ring is still abraded by the intersection between the outlet opening and the cavity containing the O-ring. The abrasion of the O-ring is reduced somewhat by reducing the compression on the O-ring and relying on water pressure to provide the requisite compressive forces, but such a valve will not seal properly under low water pressure. Furthermore, plastic valve bodies are considered by the industry to be inferior to metal valve bodies.
Prior art stop valves also suffer from inadequate handle mounting arrangements. Prior art handles are prone to failure if much torque is applied, as is often done when attempting to unstick a frozen stop valve. U.S. Pat. No. 4,609, 177 is exemplary of such a handle arrangement. Also, prior art stop valve stems rely on the valve handles to maintain the position of the stem inside of the valve body. In the event the handle is removed, the stem can be accidentally dislodged.
It is the objective of this invention to provide an improved stop valve that is not subject to the above mentioned disadvantages.
The market for stop valves is highly competitive with the result that cost reductions are important. It is accordingly the further objective of this invention to provide an improved stop valve which is functionally sound and durable and which can be manufactured more economically than those of the prior art.